1. Field of the Invention
The present invention relates to a multi-layered panel structure used as a partition wall for partitioning a large indoor space into several spaces.
2. Description of the Related Art
While partition walls are roughly divided in two types, fixed and movable, most of them are constructed by attaching face members, such as steel plates 12 and gypsum boards 13, to both surfaces of a metallic frame member 11, e.g., as shown in FIG. 18.
In order to improve the sound insulation performance of such a partition wall, measures are taken to increase the thickness of the gypsum board or to attach two gypsum boards to one side of the frame member for increasing the mass per unit area of the face member. Further, in order to suppress the coincidence phenomenon in which sound insulation performance decreases at the frequency higher than critical coincidence frequency fc that is calculated by the equation (1) shown below from the mass per unit area: m and the bending rigidity B of a face member, an example is disclosed, in which a measure is taken to attach a damping material to the inner side of a face member (see Japanese Patent Laid-Open Application No. Hei 6-221061, being hereby fully incorporated by reference). EQU fc=(C.sup.2 /2.pi.).times.(m/B).sup.1/2 (1)
where C is the velocity of sound in air.
Further, in order to suppress the low-frequency resonance transmission phenomenon in which sound insulation performance decreases by the vibrations caused at one of two face members being transmitted to the other as a result of the air layer interposed between the two face members acting as a pneumatic spring, a measure is taken to use glass wool to fill in the space between the two face members (see, e.g., Japanese Utility Model Laid-Open Application No. Sho 51-154030, being hereby fully incorporated by reference). Still further, for a movable partition wall for which a high sound insulation performance is particularly required, there is an example in which two partition walls are installed about 1 m apart from each other.
Although the sound insulation performance of a wall can be increased by increasing the mass per unit area of a face member, the wall becomes heavier and hard to install. Further, if the wall is of a movable type, it is hard to move the wall manually and thus entails much time and labor to set it up. Still further, even if the mass per unit areais, e.g., doubled, the sound insulation performance can be improved by 5 dB at most.
On the other hand, when two partition walls, each exhibiting a sound insulation performance of, e.g., 30 dB at 500 Hz, are installed about 1 m apart from each other as a double-installed wall, a sound insulation performance of about 60 dB can be obtained. However, such double-installed wall design requires not only twice as large a space for installing the walls, but also twice as large ancillary facilities such as rails for moving the partition walls. Therefore, if sufficient installation space is not available or if there are restrictions on expenditure, such double-installed wall design cannot be adopted.